Technical field
[0001] The present invention relates to the field of optical cables. In particular, the
present invention relates to an optical cable comprising a plurality of microbundles.
Background art
[0002] In the field of optical communication networks, the expression "Fiber-to-the-x" ("FTTx")
is used to denote a network architecture making use of optical fibers. In particular,
the expression "Fiber-To-The-Premises" ("FTTP") denotes the portion of the optical
communication network that reaches the premises (home, offices and the like) of the
end costumer. The expression "Fiber-To-The-Home" ("FTTH") denotes the portion of the
optical communication network that reaches the home of the end costumer.
[0003] A FTTH network is an optical communication network providing a number of end costumers
with broadband communication services, i.e. with services requiring data transmission
at a rate of more than a few Mbit/s.
[0004] Typically, a FTTH network comprises a distribution cabinet cooperating with a transport
network, a plurality of termination boxes and a plurality of optical fibers. Each
termination box is connected to the distribution cabinet by means of one or more optical
fibers.
[0005] Typically, a distribution cabinet is located in the basement of a building, in which
building the end costumers reside, whereas termination boxes are arranged at the various
building floors, within or in proximity of the apartments and/or offices of the end
costumers.
[0006] An optical cable comprising a plurality of optical fibers typically exits the distribution
cabinet. In the following of the present description, an optical cable which exits
a distribution cabinet and serves each floor of a given building to reach each end
costumer will be indicated as "in-line optical cable" or "riser cable".
[0007] FTTH installations are largely characterized by the presence of multi-dwelling units
(MDUs). Such units may comprise up to several tens of potential customers who are
concentrated onto a relatively small area and are typically distributed in a vertical
dimension.
[0008] Therefore, typically, the in-line optical cable runs through the building from the
basement up to all the building floors. The in-line optical cable is typically laid
down within a conduit, which protects the in-line optical cable.
[0009] In new buildings such conduits are generally empty and fully available for the passage
of such rising cables. On the contrary, in existing buildings the conduits are generally
at least partially occupied and it may be difficult to perform installation. In any
case, the riser cable may be typically subject to bends when it is installed in both
new and existing conduits.
[0010] Typically, an optical cable, which comprises one or more optical fibers, exits each
termination box installed at an end customer's apartment/office of the building. An
optical cable which exits a termination box is typically indicated as "drop cable".
[0011] Connecting the distribution cabinet to a termination box requires extracting at least
one in-line optical fiber from the in-line optical cable and connecting such an in-line
optical fiber to a drop optical fiber of said drop cable exiting the termination box.
The optical connection between the in-line optical cable and the drop cable is typically
made in a so-called "optical transition box".
[0012] The Applicant has faced the problem of providing an optical cable, in particular
an optical riser cable, which has a relatively reduced outer diameter while has a
high fiber count and which can be more easily bent in order to install it in conduits,
either existing conduits or new conduits. It should be remarked that providing an
optical cable having a relatively reduced outer diameter and a high number of optical
fibers are conflicting requirements.
[0013] The Applicant has also faced the problem of providing such a riser optical cable
having an optical fiber modularity, namely a fiber optical cable wherein all the optical
fibers are arranged into several groups, with each group of optical fibers comprising
one or more optical fibers. Typically, each group of optical fibers comprises the
same number of optical fibers. Each group of optical fibers could be advantageously
dedicated to a single costumer. Indeed, providing a plurality of optical fibers to
a single costumer is becoming a requirement of national telecom authorities which
want to offer more competition among telecommunication providers. This because each
single optical fiber reaching the premise of a costumer can be used by a different
telecommunication provider. After the installation of the optical cable the only operation
required to a costumer in order to change provider is to switch to the appropriate
fiber.
[0014] Several optical cables are known in the art.
[0015] For instance,
US 6,185,352 discloses a fiber optic fan-out cable having optical sub-units. The optical sub-units
are disposed about a central member, at least some of the optical sub-units each respectively
comprising a sub-unit jacket, strength fibers, and at least one respective optical
fiber ribbon therein. The optical fiber ribbon including a plurality of optical fibers,
the strength fibers generally surrounding and contacting the optical fiber ribbon
within the sub-unit jacket. A cable jacket surrounds the central member and defines
an annular space wherein the optical fiber sub-units are disposed about the central
member. The annular space including essentially no strength fibers therein outside
of the sub-unit jackets, the strength fibers being essentially located within the
optical sub-unit jacket with the respective optical fiber ribbons. One or more layers
of optical sub-units, that can be bundled with a conventional binder tape or cord,
are preferably helically (unidirectionally) or SZ stranded about the central member
in the annular space. Cable jacket has an outside diameter of about 8 mm to about
30 mm, as determined by the number of sub-units that are in the particular cable.
The number of sub-units in a cable may vary from, for example, 3 to 36.
[0016] US 7,536,071 discloses an optical cable for communication including at least one micromodule,
wherein the micromodule is blocked with respect to the propagation of water. The at
least one micromodule comprises a plurality of optical fibers, for example a bundle
of optical fibers, includes at least one optical fiber, a retaining element for housing
the at least one optical fiber, and a thixotropic filling compound arranged within
the retaining element. The micromodule comprises a plurality of optical fibers, for
example a bundle of optical fibers. The plurality of optical fibers is housed within
the retaining element in a loose manner.
[0017] US 6,067,394 discloses a modular optical transmission cable which has several reinforcement and
optical modules, each optical module having: a sheathed optical fiber, coated with:
an intermediate decoupling layer, and with a rigid shell forming a microcarrier, a
reinforcement module being associated with an optical module, the modules being molded
in an external sheath. A flexible reinforcement module is associated with at least
one optical module that is self-reinforced against compression in order to obtain
a cable having high flexibility combined with high compressive strength. The disclosure
can be applied in the field of optical fiber cables and especially that of the reinforcement
structures of such cables and fibers.
[0018] No one of the cables disclosed in the above cited prior art provides the desirable
requirements in terms of reduced diameter, high fiber counts, optical fiber modularity
and high capability to be bent for being installed in conduits, either existing conduits
or new conduits.
[0019] All requirements are particularly desirable when the optical fiber cable is used
for installing an FTTP or FTTX network.
Summary of the invention
[0020] According to the present invention it has been found an optical cable comprising
a plurality of microbundles loosely housed in an outer jacket, in which at least one
microbundle comprises an optical fiber ribbon enclosed in a coating and has an elongated
cross-section with an ellipticity ratio of between 0.5 and 1.
[0021] By elongated cross-section we mean a cross section having two orthogonal axis, in
which the dimension in the direction of one axis differs from the dimension in the
direction of the second axis.
[0022] By microbundle ellipticity we mean the ratio between the dimensions taken along two
orthogonal axis, one of which is oriented in the direction of the main dimension of
the microbundle.
[0023] By optical fiber ribbon we mean a structure having at least two optical fibers arranged
in mutual planar configuration and surrounded by an external common matrix.
[0024] Preferably, said microbundle comprises at least a strength member.
[0025] Said microbundle ellipticity enables movement and/or rotation of said at least one
microbundle within the outer jacket, thus arranging its position when the cable is
bent and avoiding microbundles packing.
[0026] The Applicant has found that a microbundle having an ellipticity less than 0.5 is
subject to packing with others microbundles. This packing compromises the ability
of extracting a selected microbundle by pulling it from an end or an opening of the
cable and decreases the ability to bend the cable. In the present description and
claims the expression "cable filling ratio" (CFR) is meant the ratio between the area
occupied by the microbundles and the internal area of the optical cable. All the areas
(of the microbundles and cable) are cross-section areas. The area occupied by the
microbundles is the sum of cross-section areas of microbundle coatings, calculated
at the outer surface of said coatings. When all the microbundles have the same size
and characteristics, the area occupied by microbundles is the area of a single microbundle,
multiplied by the number of microbundles in the optical fiber cable. The internal
area of the cable is the area, calculated at the inner surface of the outer jacket.
Such area is the area which is available for housing microbundles.
[0027] Preferably the cable filling ratio (CFR) is between 0.25 and 0.55. This enables ease
of extraction and the economy of the cable construction.
[0028] According to a first aspect, the present invention provides an optical cable, which
comprises: an outer jacket and a plurality of microbundles housed in the outer jacket,
wherein at least one of said microbundles comprises an optical fiber ribbon enclosed
in a microbundle coating, wherein a cross-section taken on a plane substantially perpendicular
to the longitudinal axis of the microbundle comprises a first dimension and a second
dimension, the first dimension being higher than the second dimension.
[0029] In one embodiment the optical cable is a riser cable. Preferably, such a cross-section
shape is symmetrical with respect to at least one first plane passing through the
longitudinal axis. More preferably, such a cross-section shape is also symmetrical
with respect to a second plane, perpendicular to the first plane and also passing
through the longitudinal axis.
[0030] In one embodiment, the microbundle coating has a substantially elliptical cross-section.
[0031] The microbundle coating comprises a minimum axis and a maximum axis, wherein a ratio,
ME, between said minimum axis and said maximum axis is 0.5≤ME<1.0.
[0032] In other embodiments, the ratio, ME, between the minimum axis and the maximum axis
is of between 0.6 and 0.9.
[0033] In still other embodiments, the ratio, ME, between the minimum axis and the maximum
axis is of between 0.6 and 0.8.
[0034] Preferably the optical fiber ribbon enclosed in the microbundle coating comprises
at least two optical fibers.
[0035] More preferably the optical fiber ribbon enclosed in the microbundle coating may
advantageously comprise four optical fibers.
[0036] The at least one microbundle may further comprise at least one strength member.
[0037] In one advantageous embodiment, the strength members of the microbundle are two and
are arranged at opposite sides with respect to said optical fibers. Each of said strength
members may be an aramidic yarn with proper yarn count
[0038] Preferably, the plurality of microbundles is loosely housed in the outer jacket.
[0039] The cable filling ratio is preferably of between 0.25 and 0.55.
[0040] A lubricant may be arranged on an external surface of said microbundle coating and/or
on the internal surface of the outer jacket.
[0041] The cable may further comprise outer jacket strength rods within the thickness of
the outer jacket.
Brief description of the drawings
[0042] The present invention will become fully clear by reading the following detailed description,
given by way of example and not of limitation, to be read by referring to the accompanying
drawings, wherein:
- Figure 1 is a schematic cross section of an optical cable according to an embodiment
of the present invention;
- Figure 2 is an enlarged schematic view of a microbundle of Figure 1; and
- Figure 3 shows the microbundle of Figure 2, its longitudinal axis and symmetry planes.
Detailed description of preferred embodiments of the invention
[0043] Figure 1 is a schematic cross section of an optical cable 1 according to an embodiment
of the present invention. Optical cable 1 comprises an outer jacket 2 and a number
of microbundles 4. In Figure 1, the number of microbundles 4 is twelve. However, this
is only an example because the cable 1 can comprise, in principle, any number of microbundles
4, either higher than twelve or lower than twelve. Preferably, the microbundles 4
are arranged in the outer jacket 2 in a loose manner. Therefore, some space is provided
between the microbundles 4 so that they can move one with respect to the other and
also with respect to the outer jacket 2.
[0044] Friction between two microbundles and between a microbundle 4 and the outer jacket
2 should be kept as low as possible, in order to improve microbundle extractability
and to prevent unwanted displacement of microbundles due to dragging originated by
the jacket. In order to keep friction as low as possible, suitable lubricants such
as talcum and/or other lubricants may be advantageously used.
[0045] The outer jacket 2 may be advantageously made of LS0H (Low Smoke Zero Halogen) materials,
or in case no specific fire safety requirements have to be fulfilled it may also be
made of LDPE, MDPE, HDPE (respectively Low, Medium and High Density Polyethylene).
Advantageously, the outer jacket 2 can have a thickness of between about 1.5 mm and
about 4.0 mm. More preferably, the outer jacket 2 can have a thickness of between
about 2.0 mm and about 3.0 mm.
[0046] As shown in Figure 1, in the thickness of the outer jacket 2 there are preferably
provided two strength rods 3. Such strength rods 3 may be made of Glass-Reinforced
Polymer (GRP) or similar composite materials. Preferably they are arranged diametrically
opposed one from the other.
[0047] Each of the microbundles 4 of the cable of Figure 1 may have different size and/or
characteristics. However, preferably, all the microbundles 4 have the same size and
characteristics.
[0048] With reference to Figure 2, each of the microbundles 4 comprises a microbundle coating
5 and a plurality of optical fibers 6. Optical fibers 6 within a microbundle 4 may
be two or more. In the embodiment shown in the Figures, the optical fibers 6 of each
microbundle 4 are four. The number of optical fibers 6 in each microbundle 4 represents
a "dose" of optical fibers 6 which can be provided to a single costumer.
[0049] Optical fibers 6 may be of any known type. For instance, they may be compliant with
any of the IEC standards or else with any of the ITU-T Recommendations, or others
as (e.g. 200 µm) coating diameter.
[0050] Preferably, as shown in Figures 1 and 2, the optical fibers 6 in the microbundle
coating 5 are arranged in a ribbon configuration. For the purposes of the present
description and claims, an optical fiber ribbon 9 is meant to be comprised by at least
two optical fibers 6 arranged in mutual planar configuration (parallel and laying
in a common plane). In such a ribbon arrangement the optical fibers 6 are surrounded
by an external common sheath or matrix 7, preferably of a polymeric material.
[0051] The optical fibers 6 of an optical fiber ribbon 9, advantageously, can be spliced
at the same time by using anyone of the commercially available ribbon splicers. This
results in an improved modular splice management which brings high cost benefits in
cable installations.
[0052] The microbundle coating 5 preferably comprises a very thin and easy-strippable thermoplastic
sheath in order to guarantee easy accessibility to the optical fibers of the microbundle.
The thickness of the microbundle coating 5 may be of about 0.05 mm to about 0.20 mm.
[0053] At least one microbundle of the plurality of microbundles 4 comprises at least one
strength member 8. Preferably, each of the microbundles 4 comprises at least one strength
member 8. Preferably, there are provided two strength members 8 on opposite sides
of the optical fiber ribbon 9 as shown in the figures. Each of said strength members
8 may be an aramidic yarn with proper yarn count (e.g. 1310 dTex).
[0054] The cross-section shape of microbundle 4 is elongated, for instance elliptical, substantially
elliptical, egg-shaped or the like. With reference to Figure 3, such a cross-section
shape is symmetrical with respect to at least one first plane S1 passing through the
longitudinal axis LA, such a cross-section shape is also symmetrical with respect
to a second plane S2, perpendicular to the first plane S1 and also passing through
the longitudinal axis LA. The cross-section of microbundle 4 comprises a first dimension
and a second dimension. The first dimension is higher than the second dimension. With
reference to Figure 3 again, the first dimension is indicated by A
max and the second dimension is indicated by A
min.
[0055] In one preferred embodiment the cross-section is substantially elliptical with a
maximum axis A
max and a minimum axis A
min. For the purposes of the present description and claims, a rate between the minimum
axis and the maximum axis will be termed as microbundle ellipticity (ME). According
to preferred embodiments of the present invention, the microbundle ellipticity ME
should be 0.5≤ME<1.0. In embodiments of the present invention, the microbundle ellipticity
ME is of between about 0.6 and about 0.9. In other embodiments, the microbundle ellipticity
ME is of between about 0.6 and about 0.8. The above microbundle strength members 8
on opposite sides of the optical fiber ribbon 9 advantageously contribute to give
the desired microbundle ellipticity ME.
[0056] The above microbundle ellipticity ME allows minimizing the dimension of a single
microbundle.
[0057] At the same time, it is desirable that the microbundle ellipticity ME is not too
low in order to avoid coupling of the microbundles within the outer jacket. In addition,
if the microbundle ellipticity ME is too low, bending the cable may become difficult
and it may become difficult also extracting the fibers from the cable.
[0058] From one side, the cable filling ratio should be kept as low as possible in order
to minimize the mechanical coupling among microbundles 4 and between the microbundles
4 and the outer jacket 2. From another side, the cable filling ratio needs to be high
enough to allow for the needed fiber density. According to embodiments of the present
invention the cable filling ratio is between 0.25 and 0.55. Preferably, the cable
filling ratio is between 0.30 and 0.50. More preferably, the cable filling ratio is
between 0.35 and 0.45.
[0059] In order to minimize the cable filling ratio but still keeping a desired low outer
cable diameter and the desired high fiber count, the thicknesses of both the outer
jacket and of the microbundle coating need to be minimized.
[0060] For instance, a cable complying with the set requirements may have the following
characteristics:
- cable outer diameter: |
17.0 mm |
- outer jacket thickness: |
2.5 mm |
- internal cable area: |
113.0 mm2 |
- microbundle coating thickness: |
0.2 mm |
- number of microbundles: |
36 |
- microbundle ellipticity: |
0.7 |
- microbundle maximum axis: |
1.4 mm |
- microbundle area: |
1.1 mm2 |
- total microbundle area: |
39 mm2 |
- cable filling ratio: |
0.35 |
[0061] The optical cable according to the present invention shows a very good behavior under
bending and provides improved resistance to mechanical damages. Therefore, installation
into existing conduits which are often at least partially occupied and are not optimized
for optical cable installation becomes possible. The improved behavior under bending
and improved resistance to mechanical damages are obtained because the microbundles
4 containing the optical fibers can arrange themselves in order to accommodate the
cable bend. In other words, when the cable according to the present invention is subject
to a bend, the microbundles having an elongated cross-section, which are preferably
loosely arranged in the outer jacket and which house ribbon optical fibers, arrange
their orientation in order to create a preferential bending plane which is compliant
with the required bending.
[0062] As a consequence of the above capability to properly arrange orientation of the microbundles,
the cable according to the present invention also shows a lower attenuation with respect
to existing microbundle cables.
[0063] The accessibility to both microbundles and optical fibers within a few meters before
and after a bend is increased in the cable according to the present invention. This
mainly because the microbundles are preferably arranged in a loose manner within the
outer jacket. A further positive consequence of the loose arrangement of microbundles
within the outer jacket is that the ability to extract a microbundle from the cable
is increased.
1. A microbundle optical cable (1) comprising:
- an outer jacket (2);
- a plurality of microbundles (4) housed in said outer jacket (2),
wherein at least one of said microbundles (4) comprises an optical fiber ribbon (9)
enclosed in a microbundle coating (5), said optical fiber ribbon (9) comprising at
least two optical fibers (6) surrounded by an external common sheath (7),
wherein said at least one microbundle (4) comprises a longitudinal axis and a cross-section
taken on a plane substantially perpendicular to said longitudinal axis, which comprises
a first dimension (Amax) and a second dimension (Amin),
wherein said first dimension (Amax) is higher than said second dimension (Amin).
2. The optical cable (1) of claim 1, wherein said microbundle coating (5) has an elongated
cross-section.
3. The optical cable (1) of claim 2, wherein said microbundle coating (5) comprises a
minimum axis (Amin) and a maximum axis (Amax), wherein a ratio, ME, between said minimum axis (Amin) and said maximum axis (Amax) is 0.5≤ME<1.0.
4. The optical cable (1) of claim 3, wherein said ratio, ME, between said minimum axis
(Amin) and said maximum axis (Amax) is of between 0.6 and 0.9
5. The optical cable (1) of claim 1, wherein said optical fiber ribbon (9) enclosed in
said microbundle coating (5) comprises four optical fibers (6) surrounded by an external
common sheath (7).
6. The optical cable (1) of any of claims 1 to 5, wherein said at least one microbundle
(4) further comprises a strength member (8).
7. The optical cable (1) of claim 6, wherein said strength member (8) comprises two strength
members (8) arranged at opposite sides with respect to said optical fibers (6).
8. The optical cable (1) of claim 7, wherein each of said two strength members (8) comprises
an aramidic yarn.
9. The optical cable (1) of any of claims 1 to 8, wherein said plurality of microbundles
(4) are loosely housed in said outer jacket (2).
10. The optical cable (1) of claim 9, wherein a cable filling ratio if of between 0.25
and 0.55.
11. The optical cable (1) of any of claims 1 to 10, wherein it further comprises a lubricant
on an external surface of said microbundle coating (5).
12. The optical cable (1) of any of claims 1 to 11, wherein it further comprises outer
jacket strength rods (3) within the thickness of said outer jacket (2).
1. Mikrobündel-Lichtwellenleiterkabel (1), das umfasst:
- eine äußere Ummantelung (2);
- eine Vielzahl von Mikrobündeln (4), die in der äußeren Ummantelung (2) aufgenommen
sind,
wobei wenigstens eines der Mikrobündel (4) ein Lichtwellenleiter-Bandkabel (9) umfasst,
das in einem Mikrobündel-Überzug (5) eingeschlossen ist, das Lichtwellenleiter-Bandkabel
(9) wenigstens zwei Lichtleitfasern (6) umfasst, die von einem gemeinsamen äußeren
Mantel (7) umschlossen sind, und
das wenigstens eine Mikrobündel (4) eine Längsachse und einen Querschnitt in einer
Ebene senkrecht zu der Längsachse umfasst, der eine erste Abmessung (Amax) und eine zweite Abmessung (Amin) umfasst,
und die erste Abmessung (Amax) höher ist als die zweite Abmessung (Amin).
2. Lichtwellenleiterkabel (1) nach Anspruch 1, wobei der Mikrobündel-Überzug (5) einen
länglichen Querschnitt hat.
3. Lichtwellenleiterkabel (1) nach Anspruch 2, wobei der Mikrobündel-Überzug (5) eine
minimale Achse (Amin) sowie eine maximale Achse (Amax) umfasst und für ein Verhältnis ME zwischen der minimalen Achse (Amin) und der maximalen Achse (Amax) 0,5≤ME<1,0 gilt.
4. Lichtwellenleiterkabel (1) nach Anspruch 3, wobei das Verhältnis ME zwischen der minimalen
Achse (Amin) und der maximalen Achse (Amax) zwischen 0,6 und 0,9 beträgt.
5. Lichtwellenleiterkabel (1) nach Anspruch 1, wobei das in dem Mikrobündel-Überzug (5)
eingeschlossene Lichtwellenleiter-Bandkabel (9) vier Lichtleitfasern (6) umfasst,
die von einem gemeinsamen äußeren Mantel (7) umschlossen sind.
6. Lichtwellenleiterkabel (1) nach einem der Ansprüche 1 bis 5, wobei das wenigstens
eine Mikrobündel (4) des Weiteren ein Verstärkungselement (8) umfasst.
7. Lichtwellenleiterkabel (1) nach Anspruch 6, wobei das Verstärkungselement (8) zwei
Verstärkungselemente (8) umfasst, die an einander in Bezug auf die Lichtleitfasern
(6) gegenüberliegenden Seiten angeordnet sind.
8. Lichtwellenleiterkabel (1) nach Anspruch 7, wobei jedes der zwei Verstärkungselemente
(8) ein Aramid-Garn umfasst.
9. Lichtwellenleiterkabel (1) nach einem der Ansprüche 1 bis 8, wobei die Vielzahl von
Mikrobündeln (4) lose in der äußeren Ummantelung (2) aufgenommen sind.
10. Lichtwellenleiterkabel (1) nach Anspruch 9, wobei ein Kabel-Füllgrad zwischen 0,25
und 0,55 beträgt.
11. Lichtwellenleiterkabel (1) nach einem der Ansprüche 1 bis 10, wobei es des Weiteren
ein Schmiermittel an einer Außenfläche des Mikrobündel-Überzugs (5) umfasst.
12. Lichtwellenleiterkabel (1) nach einem der Ansprüche 1 bis 11, wobei es des Weiteren
Verstärkungsstäbe (3) der äußeren Ummantelung innerhalb der Dicke der äußeren Ummantelung
(2) umfasst.
1. Câble optique à microfaisceaux (1) comprenant :
- une enveloppe extérieure (2) ;
- une pluralité de microfaisceaux (4) logés dans ladite enveloppe extérieure (2),
dans lequel au moins un desdits microfaisceaux (4) comprend un ruban de fibres optiques
(9) incorporé dans un revêtement de microfaisceaux (5), ledit ruban de fibres optiques
(9) comprenant au moins deux fibres optiques (6) entourées par une gaine externe commune
(7),
dans lequel ledit au moins un microfaisceau (4) comprend un axe longitudinal et une
section transversale prise sur un plan sensiblement perpendiculaire au dit axe longitudinal,
qui comprend une première dimension (A
max) et une seconde dimension (A
min),
dans lequel ladite première dimension (A
max) est supérieure à ladite seconde dimension (A
min).
2. Câble optique (1) selon la revendication 1, dans lequel ledit revêtement de microfaisceaux
(5) a une section transversale allongée.
3. Câble optique (1) selon la revendication 2, dans lequel ledit revêtement de microfaisceaux
(5) comprend un axe minimum (Amin) et un axe maximum (Amax), dans lequel un rapport, ME, entre ledit axe minimum (Amin) et ledit axe maximum (Amax) est 0,5 ≤ ME < 1,0.
4. Câble optique (1) selon la revendication 3, dans lequel ledit rapport, ME, entre ledit
axe minimum (Amin) et ledit axe maximum (Amax) est entre 0,6 et 0,9.
5. Câble optique (1) selon la revendication 1, dans lequel ledit ruban de fibres optiques
(9) incorporé dans ledit revêtement de microfaisceaux (5) comprend quatre fibres optiques
(6) entourées par une gaine externe commune (7).
6. Câble optique (1) selon l'une quelconque des revendications 1 à 5, dans lequel au
moins un microfaisceau (4) comprend en outre un élément de renfort (8).
7. Câble optique (1) selon la revendication 6, dans lequel ledit élément de renfort (8)
comprend deux éléments de renfort (8) agencés sur des côtés opposés par rapport aux
dites fibres optiques (6).
8. Câble optique (1) selon la revendication 7, dans lequel chacun desdits deux éléments
de renfort (8) comprend un fil aramide.
9. Câble optique (1) selon l'une quelconque des revendications 1 à 8, dans lequel ladite
pluralité de microfaisceaux (4) sont logés de façon lâche dans ladite enveloppe extérieure
(2).
10. Câble optique (1) selon la revendication 9, dans lequel un rapport de bourrage de
câble est entre 0,25 et 0,55.
11. Câble optique (1) selon l'une quelconque des revendications 1 à 10, dans lequel il
comprend en outre un lubrifiant sur une surface externe dudit revêtement de microfaisceaux
(5).
12. Câble optique (1) selon l'une quelconque des revendications 1 à 11, dans lequel il
comprend en outre des tiges de renfort d'enveloppe extérieure (3) à l'intérieur de
l'épaisseur de ladite enveloppe extérieure (2).